1. Field of the Invention
This invention relates to fluorescent light emitting devices and more particularly to such devices in which the ionized, light emitting gas follows a non-direct, non-linear path.
2. Brief Description of the Prior Art
Fluorescent lighting in the form of gas discharge tubes containing ionizable gas is well known. This lighting form works as follows: an elongate tube with an electrode at each end is filled with an ionizable gas. When a power source is connected across the electrodes ionization of the gas occurs causing the gas to glow and emit light.
In what is commonly called "cold cathode" lighting apparatus, a high voltage is applied across the two electrodes; this voltage being sufficiently high to cause ionization of the gas directly. As opposed to this, "hot cathode" lamps operate by imparting heat energy to the gas at each electrode; this heat energy being sufficient to cause localized ionization of the gas at the electrode. Thereafter, a much lower voltage, as compared to that used in cold cathode lamps, is applied across the electrodes to maintain ionization of the remainder of the gas volume.
It is usual for the interior surface of the gas discharge tube to be coated with a fluorescent material such as phosphorous which fluoresces as a result of the glowing ionized gas. It is this layer of phosphorous that emits the commonly known fluorescent light and has the effect of making the expanse of light corresponding to the band of ionization more uniform and spread out than the ionization band itself. Typically gas discharge tubes contain a noble gas such as neon or argon.
The relative advantages of gas discharge lighting devices are well known and include: low heat generation, lower energy costs for a given intensity of lighting and long bulb life.
It is a characteristic of gas discharge lamps that the path of ionization follows the shortest route between the two electrodes. Even with the dispersion effect caused by the fluorescent lining on the inside of the tubes, the lighting effect of gas discharge tubes is at best in the form of a narrow band of light.
The disadvantage of this characteristic is that the use of gas discharge lighting devices in situations where a non-linear or non-direct light path is required, needs special engineering. An example of this is in the decorative or sign writing applications where the tube, in which the gas is contained, must be bent or shaped into the desired configuration.
Alternatively, as has been proposed in U.S. Pat. No. 4,584,501 (Cocks et al.), a configured or shaped ionization chamber can be carved into thick glass plates.
Both these methods of shaping the ionization path of the gas are in fact methods of configuring or shaping the ionization chamber such that the ionization path is forced to follow a path dictated by the shape of the chamber. Both these methods have the disadvantage that they are expensive to implement.
In addition there are other instances where a uniform sheet of lighting is required. An example of this is the office environment where a plurality of fluorescent lighting tubes are used in combination with reflectors and/or light diffusers to produce an approximation of a sheet of light. Although such systems are adequate it would be better and less complicated if the combination were to be replaced by a single sheet light element which produces a uniform sheet of lighting.